In the production of automobiles base or prime coated automobile bodies are wet-sanded prior to the final color coating step. An apparatus installed in such a wet-sanding line typically comprises a conveyor for conveying a series of automobile bodies and a stand equipped with a plurality of abrasive means rotatable with their axes of rotation in perpendicular to the direction of conveyance of the automobile bodies, and is designed so that the rotating abrasive means may be brought in contact with the surfaces of each automobile body as it progresses past the stand. However, the structure and mechanism, which have heretofore been adopted for bringing the abrasive means in contact with the automobile body, are limitedly successful as to following changes in cross-section of the automobile body as it progresses past the abrasive means and ensuring a constant abrasion pressure over the broadest possible areas of the surfaces of the automobile body.
In the accompanying drawings:
FIGS. 1 through 6 are to illustrate the state of the prior art. FIG. 1 schematically shows a mechanism disclosed in U.S. Pat. No. 3,237,348 to A.Block for bringing an overhead abrasive brush 1 in contact with the surface of the roof 2 of the automobile body. According to this U.S. patent the single transverse overhead abrasive brush 1 is carried by a pair of arms 3 (one of which is shown in FIG. 1) that are swung by a pair of power cylinders 4 (one of which is shown in FIG. 1) between a first upper operating position for processing the roof 2 and a second lower operating position for processing a trunk 5, and mounted on the arms 3 by pivoted bell cranks 6 (one of which is shown in FIG. 1) which may be rocked by power cylinders 7 (one of which is shown in FIG. 1) to an upper idle position. During operation the rotating brush 1 is forced against the surface of the roof 2 being processed by introducing air of a predetermined pressure into the power cylinders 7 of the bell cranks 6.
However, a transverse cross-sectional configuration of a given automobile body normally changes as it progresses past the abrasive means. FIG. 2 is a cross-sectional view of a central portion of the roof being processed, taken as indicated by the lines II--II of FIG. 1, while FIG. 3 is a similar view of a rear portion of the roof being processed, taken as indicated by the lines III--III of FIG. 1. As seen from FIGS. 2 and 3, variations of the transverse cross-sectional configuration of the body result in variations of the width of the brush in contact with the body from W.sub.1 to W.sub.2, and in turn result in variations of the area of the brush in contact with the body. Accordingly, even if the brush is forced against the body by a constant pressure in the cylinder 7, the abrasive pressure per unit area of the brush inevitably varies, leading to variations of the abrasion reduction in thickness. Obviously, uneven abrasion reduction in thickness of the prime coat is undesirable for obtaining a uniform final color coat.
Further, it is undesirable that there remain untreated areas as indicated by numeral 8 in FIG. 3, and an atempt to bring the brush in contact with those areas 8 by exerting a higher pressure on the brush will result in variations of the distance (radius) from the axis 9 of rotation of the brush to the face of the brush at which contacts with the surface of the automobile body between the central portions of the brush and the portions of the brush where it contacts with the areas 8, again leading to variations of the abrasion reduction in thickness.
For better accommodation to a given transverse cross-sectional configuration of the automobile body, U.S. Pat. No. 3,237,348 proposes use of abrasive brushes of various profiles such as illustrated in FIGS. 4 and 5. When an automobile body having stripes on its roof is to be processed, an overhead abrasive brush such as shown in FIG. 6 will have to be used. Each of the brushes shown in FIGS. 4-6, has different radii and thus different peripheral speeds from place to place, again leading to variations of the abrasive reduction in thickness. In addition, it would reduce the productivity to prepare a number of overhead abrasive brushes having various profiles and to install a suitable one on the machine in accordance with the particular cross-sectional configuration of the given type of the automobile body.
Thus, no special measure has been taken in the prior art regarding control of the abrasive pressure in response to changes of the transverse cross-sectional configuration of complex curvature of the roof of the automobile body, and in consequence variations of the abrasion reduction in thickness between the central and side zones longitudinally of the roof as well as between the central and front or rear portions transversely of the roof have been unavoidable, often leading to occurrence of areas insufficiently abraded and those excessively abraded or even badly impaired.
On the other hand an automobile manufacturer is manufacturing automobiles of different models and types. Since it is uneconomical to construct an abrasive apparatus for every model of the automobile bodies, one single abrasive line in the factory has to treat automobile bodies of different models. However, the prior art apparatus is not designed so that a change of the set operative positions of the overhead abrasive brush and a change of the set abrasive pressure may be effectively made immediately in response to change of the model of automobile bodies to be processed, and thus upon every change of the model of automobile bodies to be processed it has been necessary to stop the line and to re-set the operative positions of the brush 1 and the pressure of air to be maintained in the cylinder 7 so that a new series of automobile bodies of the changed model may be properly processed. Obviously, the necessity of such re-setting procedures would be disadvantageous. Even so re-set, there still remains a problem of uneven abrasion reduction in thickness, as discussed hereinabove.
Wet-standing in advance of the final color coating is an important step which substantially affects the quality of the color coat finish. Accordingly, an improved abrasive apparatus, by which the broadest possible areas of the surfaces of each of successively conveyed automobile bodies may be uniformly processed under a constant abrasive pressure with a uniform abrasion reduction in thickness, is desired in the art. Especially because of a recent tendency that automobiles of various body models, such as sedan, coupe and van, are manufactured in one automobile manufacturing factory at the same period of time and that with the same model a change of type is frequently effected within a relatively short interval of time, an improved abrasive apparatus which may cope with such changes of model and type, and ensure a uniform automatic abrasive treatment over the broadest possible areas of the surfaces of automobile bodies, is intensively desired in the art.